Method of preparing a foamed lactone polymer



United States Patent 7 Claims. (Cl. 260-25) This application is acontinuation, of Serial No. 156,- 994, filed Dec. 4, 1961, now PatentNo. 3,224,982, entitled, Method of Preparing a Foamed Lactone Polymer.

The invention relates to foamed polymers of certain vinyl copolymers.More particularly, it is concerned with a process for producing foamedpolymeric lactone copolymers and the products produced thereby.

The production of polymeric foams is well known. Generally, these foamsare produced by releasing added, dissolved, or entrapped gas from apolymer melt so as to form small bubbles and thus produce a foamedstructure. Presently, polystyrene is foamed by compounding the resinwith a low boiling hydrocarbon such as pentane to form a mixture whichproduces a foam when heated above the boiling point of the hydrocarbonand the softening point of the polymer. Vinyl chloride resins are foamedby forcing a gas such as carbon dioxide, ethane, or methyl chlorideunder pressure into a melt of the polymer and then reducing the pressureof the melt whereby the gas expands and foams the polymer. Inessentially all of the known methods, however, the addition of anexternal foaming agent is a necessary step.

It has now been found that certain vinyl polymers can be foamed withoutthe addition of an external foaming agent. This foaming is accomplishedby utilizing a chemical reaction novel to certain polymeric materials.

The vinyl polymers which can be foamed by the process of this inventionare those uniform polymers containing units of the formula:

wherein R is an alkyl radical containing from 1 to 4 carbon atoms, aphenyl radical, or a CH COOR"; R is a hydrogen atom, a methyl radical,or a halogen atom such as chlorine, bromine, fluorine, or iodine; R" isan alkyl radical containing from 1 to 4 carbon atoms or atetrahydrofurfuryl radical; and X is a halogen atom as defined above.

The vinyl copolymers that are suitable for use in this invention containthe unit (I) in the polymer chain at concentrations of at least l0'molepercent. The preferred copolymers that the uniform copolymers whichconsist entirely of such repeating units, that is to say, a uniformcopolymer containing the repeating units throughout the polymer chain.For example, a copolymer of vinyl chloride and methyl methacrylate madeup of repeating vinyl chloride (VCl) and methyl methacrylate (MMA) unitsrepresented as follows:

Patented May 23, 1957 copolymer is one which does not have alternatingVCl and MMA units, as represented by the formula:

It can be seen that although the uniform (II) and nonuniform (III)copolymers both contain five methyl methacrylate units and five of theunits represented by Formula I whereas the nonuniform copolymer has onlytwo such units. Since those copolymers having the greatest number ofunits represented by the Formula I produce the most desirable foams, itis important that the uniformity of the copolymer be at a maximum.

In the process of the instant invention, the copolymers to be foamed areheated under pressure for a period of time sufiicient to release an R"Xcompound and at the same time form a lactone ring in the polymer chain.The reaction can be represented in its simplest form by the From thisequation it becomes obvious why it is desirable to have a uniform acopolymer as possible. The more uniform the copolymer, the more RXcompound formed, resulting in a better foaming action and a large numberof lactone rings in the polymer chain.

The uniformity of the copolymers can be controlled and uniformcopolymers can be prepared by continuously feeding the fastercopolymerizing monomer to the polymerization reaction throughout theduration of the polymerization at such a rate as to keep the ratio ofpolymerizing comonomers in the reactor as constant as possible. Thiswill lead to polymer chains having the highest degree of uniformity andtherefore produce foams with the greatest of ease and the greatestdegree of lactonization. Copolymers having a high degree of uniformitycan also be produced by carrying out the polymerization reaction to alow conversion so that the comonomer ratio in the reactor is notappreciably altered. The copolymers are readily produced by emulsion,suspension, or bulk processes known in the art. However, as indi catedabove, the degree of uniformity is increased by following the statedsuggestions.

Among the copolymers that can be used are the vinyl chloride/methylmethacrylate copolymer, vinyl chloride/ ethyl methacrylate copolymer,vinyl chloride/butyl methylacrylate copolymer, vinyl bromide/methylmethacrylate copolymer, vinyl fluoride/methyl methacrylate c0- polymer,vinyl iodide/methyl methacrylate copolymer, vinylidene chloride/methylmethacrylate coploymer, vinylidene chloride/butyl methacrylatecopolymer, vinyl chloride/dimethyl itaconate copolymer, vinyl chloride/tetrahydrofurfuryl methacrylate/methyl methacrylate terpolymer, and thelike.

The suitable copolymers are those containing in the polymeric chain fromabout 5 to mole percent of polymerized units of the formula --CH2CI]R'obtained from the polymerization of a vinyl or vinylidene halide withfrom about 95 to 5 mole percent of polymerized ester units of theformula from an ester; preferably the copolymers are those containingfrom about 20 to 80 mole percent polymerized vinyl vinylidene halideunits and from 80 to 20 mole percent polymerized ester units; With themost preferred copolymers being those containing from about 40 to 60mole percent polymerized vinyl or vinylidene halide units and from 60 to40 mole percent polymerized ester units.

Among the vinyl halide and vinylidene halide that can be used one canmention vinyl chloride, vinyl bromide, vinyl fluoride, vinyl iodide,vinylidene chloride, vinylidene bromide, vinylidene fluoride, vinylideneiodide, and the like.

Among the esters which can be used to produce the copoly mers suitablefor foaming by the process of this invention one can mention methylmethacrylate, ethyl methacrylate, butyl methacrylate, methyl alpha-ethylacrylate, methyl alpha-propyl acrylate, methyl alpha-butyl acrylate,ethyl alpha-ethyl acrylate, propyl alpha-ethyl acrylate, butylalpha-ethyl acrylate, tetrahydrofurfuryl methacrylate, dimethylitaconate, diethyl itaconate, dipropyl itaconate, dibutyl itaconate, andthe like.

According to this invention the polymers are foamed by a two-stepprocess. The first step is a pyrolysis step during which period thepolymer is heated under pressure at elevated temperatures to liberatethe R"X compound while at the same time undergoing lactonization. In thesecond step foaming is permitted to take place by releasing the pressurewhile the temperature is maintained above the softening point of thepolymer.

The pyrolysis is carried out at a temperature from about 100 C. to 250C., preferably from about 150 C. to 200 C. at the autogenous pressure inthe recator up to about 7,500 p.s.i.g. or more. The pyrolysis is carriedout for a period of time sufficient to cause lactonization and will varydepending upon the particular polymer being used, the temperature, andthe pressure. Normally the time required is inversely proportional tothe temperature used. The pyrolyzed polymer is caused to foam byreleasing the pressure while the temperature is maintained at from about50 C. to 200 C., preferably from about 80 C. to 160 C.

The polymer foam can be produced in readily available equipment, theonly requirement being that the vessels used for pyrolysis be capable ofmaintaining the desired pressure and prevent the leakage of the releasedRX compound produced during the pyrolysis. Apparatus as simple as a moldand a heated hydraulic press can be used. With this type of apparatus,the polymer is heated in the mold under pressure and at an elevatedtemperature until the R"X compound is released and lactonization hasoccurred. The mold is then cooled to the desired temperature for foamingand the hydraulic pressure is suddenly released whereupon the foamedstructure pops out of the mold. This technique is known as the moldexpansion technique. In a modification of this technique after the R"Xcompound has been liberated and lactonization has taken place, the moldis cooled to room temperature and the polymer is permitted to solidify.The solidified polymer will not foam even though RX compound isentrapped in it since the polymer has been cooled below its softeningpoint. This cooled plaque can then be placed in an oven or other heatedapparatus and heated to the desired temperature whereupon the entrappedgases expand and a foam is produced. The cooled plaque can, if desired,be placed in a shaped mold and heated whereupon it foams to take on theshape of the mold. This latter heating step can also be performed bysteam or radio frequency heating rather than oven heating.

An alternative procedure for producing the foamed polymer is to extrudeit directly from the unpyrolyzed polymers. For this purpose amulti-stage, preferably a two-stage, extruder is used. In the firststage the polymer is heated at a temperature high enough for liberationof the R"X compound and lactonization to take place while the secondstage of the extruder is maintained at the temperature required for foamproduction. As the polymer passes through the first heating stage, it ispyrolyzed to the desired lactone structure with the liberated RXcompound remaining entrapped in the molten polymer. The molten polymeris then cooled in the second stage of the extrude to the desired foamingtemperature and passes out through an orifice where the pressure of theliberated R"X is released producing the desired foamed shape. Thislatter technique is exceptionally desirable in the production of afoamed insulation of an electrical conductor.

The foamed polymers produced by this invention can be used in manyapplications to which foams are applied; for example, they can be usedas insulating materials, as cushioning materials, as interlayers in theproduction of laminted wall panels, and so forth. The lactone polymersof this invention find special utility as molding compounds for theproduction of sound records.

The foamed polymers of this invention have densities of from about 1pound per cubic foot to about 30 pounds per cubic foot. It was foundthat the formation of the lactone structure in the polymer backbonegreatly increased the softening point of the foamed polymer over that ofthe unpyrolyzed and nonfoamed polymer with essentially no change indegree of polymerization. The apparent melting points of the pyrolyzedresins are similar to those of the unpyrolyzed resins. It was also foundthat the foams of those polymers originally high in vinyl chloridecontent behaved quite similarly to vinyl chloride, being nonflammableand soluble in common poly(vinylchloride) solvents such as cyclohexanoneand tetrahydrofuran. The foams of polymers originally high in methylmethacrylate content were after pyrolysis still soluble in ketones oraromatics and burned rapidly properties common to poly(methy1methacrylate). A pyrolyzed copolymer containing very few halogen orunreacted ester groups was unaffected by immersion at room temperaturein kerosene or heptane or after a fourhour immersion at 100 C. in theseliquids. Such foams are obtained by the pyrolysis of a 50:50 molepercent copolymer of vinyl chloride and methyl methacrylate.

It was found that the pyrolysis of the uniform copolymers by the processof this invention was smooth, rapid, and almost statisticallyquantitativethat is to say that during pyrolysis the lactonizationreaction was essentially complete, with the liberation of 1 mole of R"Xcompound for about 85 percent of the units represented by Formula I. Inthose instances where some nonuniforrnity exists in the polymer chain,the theoretical amount of R"X compound evolved will be less than thestatistically quantitative value. Gas analysis of the liberated gasshows that the gas consisted almost entirely of R"X compound when auniform polymer as defined in this invention was pyrolyzed. When a blendof polymers, for example, -a blend of poly (vinyl chloride) andpoly(methyl methacrylate) was pyrolyzed, gas analysis on the liberatedgases showed that 5.5 mole percent was methyl chloride, 54.1 molepercent was hydrogen chloride, 35.7 mole percent was methylmethacrylate, and 5.4 mole percent was benzene. This indicates that apolymer blend, although yielding a small amount of methyl chloride, orR"X compound, mainly decomposes to give the expected pyrolysis productsof homopolymer decomposition: benzene and hydrogen chloride frompoly(vinyl chloride) and methyl methacrylate from poly(methylmethacrylate). The nonuniform copolymer, prepared by polymerizing amixture of methyl methacrylate and vinyl chloride to complete conversionby conventional procedures, behaved upon pyrolysis much like the blendof the two homopolymers and not at all like the uniform copolymers.

The pyrolysis of poly(methyl alpha-chloroacrylate) by V the process ofthis invention resulted in products other than those which would beobtained by the lactonization reaction and it was found that theliberated gas contained hydrogen chloride, benzene, methanol, and carbondioxide in addition to the methyl chloride. It was also observed thatthe pyrolysis of this homopolymer proceeded at a much slower rate thanthat of the uniform methyl methacrylate/vinyl chloride copolymers. Thepyrolysis of the uniform polymers is an intramolecular reaction andcyclization to the lactone in which there is no change in the de ree ofpolymerization of the product, whereas the pyrolysis of the homopolymeror of the blends results in molecular weight degradation andcrosslinking a evidenced by the nature of the gaseous by-productsrecovered and the insolubility of the resulting polymeric products.

When the vinyl or vinylidene halide employed was the bromide rather thanthe chloride, the pyrolysis reaction was much more rapid when the sameester comonomer was used in producing the polymer. It also was observedthat the vinylidene halides are more reactive than the vinyl halides.

The R" group on the ester does not appear to have any effect on the rateor efiiciency or lactonization during pyrolysis. However, it was foundthat the R group should preferably be an electron repelling group suchas defined above since electron-withdrawing groups such as halogen atomscauses undesirable side reactions. The uniform copolymers can be blendedwith fillers or with other polymers and the blends can then be treatedby the process of this invention to produce foamed polymers; they canalso be incorporated with plasticizers and pyrolyzed to produce flexiblefoams.

The following examples further serve to illustrate this invention butare not to be considered as limiting it in any manner whatsoever.

Example 1 A uniform copolymer (20 grams) containing 29 percent by weightof polymerized methyl methacrylate and 71 weight percent polymerizedvinyl chloride was placed in a 2-inch mold in a hydraulic press andheated to 190 C. over a ten-minute period. The pressure was initially2,000 p.s.i.g. but increased to about 3,000 p.s.i.g. at the end of theheating period. The mold Was cooled to room temperature and the plaquewas removed. This pyrolyzed plaque had a density of about 60 pound percubic foot and it appeared very similar to a regular vinyl plaque butwas slightly more flexible. The polymer was a lactone polymer containingunits of the formula The plaque was placed in a 100 C. oven for tenminutes during which time it foamed to produce a uniform cellular foamwhich had a densitp of 3 pounds per cubic foot.

Example 2 A 20 gram sample of 29.8/70.2 weight percent vinylchloride/methyl methacrylate copolymer was placed in a 2-inch diametermold at 80 C. and brought to 4,000 p.s.i.g. pressure by means of ahydraulic press. The mold was steam heated and forty minutes later thetemperature was 174 C. and the pressure had increased to 6,000 p.s.i.g.The steam was turned off and in twenty-five minutes the temperaturedecreased to 120 C. and the pressure to 5,250 p.s.i.g. The hydraulicpressure was then released suddenly whereupon the mold popped apart bythe foaming of the lactone polymer. The foam had a closed cell structureand a density of 1.58 pounds per cubic foot.

Example 3 In a manner similar to that described in Example 1 a uniformcopolymer containing 71 weight percent polymerized vinyl chloride and 29weight percent polymerized 6 methyl methacrylate was lactonized andfoamed. The foam was of closed cell structure and had a density of 1.89pounds per cubic foot.

Example 4 A ram-extruder was charged with about 50 grams of a 21/79weight percent uniform vinyl chloride-methyl methacrylate copolymer. Thechamber which contained the copolymer was closed 01f and heated to 190C. during which time the ram was pushed against the sample at a pressureof about 1,000 p.s.i.g. When this temperature was reached, afterapproximately ten minutes, the heat was turned off and the temperaturewas permitted to decrease to 150 C. At this point the valve at the endof the extruder was opened, releasing the lactone polymer in the form ofa foamed rod having a density of 2.22 pounds per cubic foot.

Example 5 A blend containing equal weights of (A) a poly- (vinylchloride) homopolymer having a reduced viscosity of about 1.5 and (B) a70.6/29.4 weight percent uniform vinyl chloride/methyl methacrylate wasprepared by mixing the two together in a Waring Blendor. This blend waslactonized and foamed in a manner similar to that described in Example2, using a pyrolysis temperature of 184 C. and a pressure of 6,750p.s.i.g. and foaming at C. after the pressure had decreased to 6,000p.s.i.g. The foam had a density of 7.8 pounds per cubic foot.

Example 6 A- blend was prepared from equal Weights of (A) a 92/8 weightpercent vinyl chloride/ethylene copolymer and (B) a 70.6/29.4 weightpercent vinyl chloride/methyl methacrylate copolymer in the same manneras described in Example 5. The blend was lactonized and foamed in amanner similar to that described in Example 5 with the pyrolysistemperature being 188 C. and the pressure 7,000 p.s.i.g. The pyrolyzedcopolymer was foamed at C. after the pressure had dropped to 6,500p.s.i.g. The foam had a density of 4.9 pounds per cubic foot.

Example 7 A 66.5/33.5 weight percent uniform vinyl chloride/ ethylmethacrylate copolymer was lactonized and foamed as described inExample 1. The pyrolysis and lactonization reaction was carried out forten minutes at 195 C. and 5,000 p.s.i.g.; and the foaming reaction wasconducted at 100 C. The foam produced had a density of 1.9 pounds percubic foot.

Example 8 A 66.8/33.2 weight percent uniform vinylidene chloride/methylmethacrylate copolymer was reacted in a manner similar to that describedin Example 1. The lactonization was carried out at 195 C. and 5,000p.s.i.g. for two minutes; and the resulting mixture was foamed at 100 C.The lactone polymer contained units of the formula The foam had adensity of 2.6 pounds per cubic foot.

Example 9 A sample of an 80/20 weight percent uniform vinylchloride/dimethyl itaconate copolymer having a reduced viscosity of0.62, as measured from a 0.2 percent solution of the copolymer incyclohexanone at 30 C., was placed in a 2-inch diameter mold at 50 C.and brought to 4,000 p.s.i.g. by means of a hydraulic press. Thetemperature was raised to 180 C. with a superheated steam and thepressure in the mold increased to 6,000 p.s.i.g. After cooling the moldto 105 C., the hydraulic pressure was suddenly released whereupon themold popped apart by the foaming of the lactone polymer. The foam had adensity of 6.24 pounds per cubic foot.

It was observed that the process of this reaction progresses in twostages with the uniform copolymers of dimethyl itaconate and vinylchloride. The first stage takes place at about 110 C. to form asix-membered lactone ring as follows:

In the second stage the lactone produced at temperatures above about 110C. when heated at temperatures above about 150 C. produces a secondlactone ring, this one containing five members in the ring, as follows:

(3 2 0 A Coumpound A CHrCHCH2-O-CHa-CH 150C I (I) O The same reactionoccurs with other vinyl halides or vinylidene halides.

Example An 18/50/32 weight percent uniform vinyl chloride/ methylmethacrylate/tetrahydrofurfuryl methacrylate terpolymer having a reducedviscosity of 1.25 was placed in a 2-inch diameter mold at 60 C. andborught to 4,000 p.s.i.g. pressure by means of a hydraulic press. Thepress was heated by steam and after one hour the temperature of the moldwas 187 C. and the pressure was 7,250 p.s.i.g. The steam was turned offand the mold was cooled to a temperature of 120 C. while the pressuredropped to 6,500 p.s.i.g. The hydraulic pressure was then releasedsuddenly, whereupon the mold popped open by the foaming of the lactonepolymer. The foam was of uniform cellular structure, had a white color,and had a density of 4.6 pounds per cubic foot.

Example 11 A 63.1/ 36.9 weight percent uniform vinyl bromide/ methylmethacrylate copolymer having a reduced viscosity of 0.12 was placed ina 1% inch compression mold at 30 C. The mold was heated over atwenty-five minute period to 170 C. during which period the pressure inthe mold increased to 2,150 p.s.i.g. Thereafter the mold was cooled to100 C.; the press pressure was suddenly released to allow the foamingmaterial to pop the mold apart. The lactone polymer foam had a densityof 5.9 pounds per cubic foot.

Attempts were made to foam monuniform copolymers as obtained byconventional emulsion polymerization procedures wherein the initialmonomers charge is reacted until the polymerization reaction iscompleted. To vinyl chloride/ methyl methacrylate copolymers were usedcontaining 70 and 30 weight percent vinyl chloride, respectively. Eachsample was pyrolyzed at 190 C. and 5,000 p.s.i.g. for ten minutes, themold was cooled, and the plaque was removed as described in Example 1.The plaques were then placed in a C. oven in an attempt to foam thepyrolyzed resins. Only slight bubbling occurred with no foam beingproduced from either polymer sample. This is in contrast to the resultsobtained in the above examples which were carried out under similarconditions and which produced satisfactory foams from the uniformcopolymers. In addition, a vinyl chloride/ ethyl acrylate copolymercontaining 76.7 weight percent of the vinyl chloride monomer was treatedin a manner similar to that described in Examples 7 and 8. No evidenceof foaming was observed. This substantiates the necessity of having an Rsubstitutent on the ester monomer used in producing the copolymers.

What is claimed is:

1. A process for producing a lactone-containing foam which comprisesheating at from 100 C. to 250 C. and at a superatmospheric pressure upto 7,500 p.s.i.g. a uniform copolymer selected from the group consistingof:

(a) vinyl chloride/methyl methacrylate,

(b) vinyl chloride/methyl methacrylate in homogeneous admixture withpoly(vinyl chloride),

(c) vinyl chloride/methyl methacrylate in homogeneous admixture with avinyl chloride/ethylene copolymer,

(d) vinyl chloride/dimethyl itaconate,

(e) vinyl chloride/methyl methacrylate/tetrahydrofurfuryl methacrylate,and

(f) vinyl bromide/methyl methacrylate so as to produce the lactonepolymer thereof together with the corresponding methyl halide, and thenreleasing the pressure at from about 50 C. to 200 C.

2. A process for producing a lactone-containing foam which comprisesheating at from 100 C. to 250 C. and at a pressure up to 7,500 p.s.i.g.a uniform vinyl chloride/methyl methacrylate copolymer so as to producethe lactone polymer thereof together with methyl chloride, and thenreleasing the pressure at from about 50 C. to 200 C. to foam saidlactone polymer.

3. A process for producing a lactone-containing foam which comprisesheating at from 100 C. to 250 C. and at a pressure up to 7,500 p.s.i.g.a blend of a uniform vinyl chloride/ methyl methacrylate copolymer withpoly- (vinyl chloride) so as to produce the lactone polymer thereoftogether with methyl chloride, and then releasing the pressure at fromabout 50 C. to 200 C. to foam said lactone polymer.

4. A process for producing a lactone-containing foam which comprisesheating at from 100 C. to 250 C. and at a pressure up to 7,500 p.s.i.g.a blend of a uniform vinyl chloride/ methyl methacrylate copolymer witha vinyl chloride/ethylene copolymer so as to produce the lactone polymerthereof together with methyl chloride, and then releasing the pressureat from about 50 C. to 200 C. to foam said lactone polymer.

5. A process for producing a lactone-containing foam which comprisesheating at from 100 C. to 250 C. and at a pressure up to 7,500 p.s.i.g.a uniform vinyl chloride/dimethyl itaconate copolymer so as to producethe lactone polymer thereof together with methyl chloride, and thenreleasing the pressure at from about 50 C. to 200 C. to foam saidlactone polymer.

6. A process for producing a lactone-containing foam which comprisesheating at from 100 C. to 250 C. and at a pressure up to 7,500 p.s.i.g.a uniform vinyl chloride/ methyl methacrylate/tetrahydrofurfurylmethacrylate polymer so as to produce the lactone polymer thereoftogether with methyl chloride, and then releasing the pressure at fromabout 50 C. to 200 C. to foam said lactone polymer.

7. A process for producing a lactone-containing foam which comprisesheating at from 100 C. to 250 C. and at a pressure up to 7,500 p.s.i.g.a uniform vinyl bromide/ methyl methacrylate copolymer so as to producethe lactone polymer thereof together with methyl bromide,

and then releasing the pressu e at from about 50 C. to 3,044,970 7/1962Bai eistir et a1 2602.5 Said lactone Pdymar- 3,049,521 8/1962 Burkholder26086.3

References Cited by the Examiner UNITED STATES PATENTS 5 MURRAY TILLMAN,Przmary Exammer. 2,537,881 1/1951 Dickey 26088.3 I. C. BLEUTGE,Assistant Examiner.

2,684,341 7/1954 Anspon et a1. 2602.5

1. A PROCESS FOR PRODUCING A LACTONE-CONTAINING FOAM WHICH COMPRISESHEATING AT FROM 100*C. TO 250*C. AND AT A SUPERATMOSPHERIC PRESSURE UPTO 7,500 P.S.I.G. A UNIFORM COPOLYMER SELECTED FROM THE GROUP CONSISTINGOF: (A) VINYL CHLORIDE/METHYL METHACRYLATE, (B) VINYL CHLORIDE/METHYLMETHACRYLATE IN HOMOGENEOUS ADMIXTURE WITH POLY (VINYL CHLORIDE), (C)VINYL CHLORIDE/METHYL METHACRYLATE IN HOMOGENEOUS ADMIXTURE WITH POLY(VINYL CHLORIDE), (C) VINYL CHLORIDE/METHYL METHACRYLATE IN HOMOOGENEOUSADMIXTURE WITH A VINYL CHLORIDE/ETHYLENE COPOLYMER, (D) VINYLCHLORIDE/DIMETHYL ITACONATE, (E) VINYL CHLORIDE/METHYLEMETHACRYLATE/TETRAHYDROFURFURYL METHACRYLATE, AND (F) VINYLBROMIDE/METHYL METHACRYLATE SO AS TO PRODUCE THE LACTONE POLYMERTGHEREOF TOGETHER WITH THE CORRESPONDING METHYL HALIDE, AND THENRELEASING THE PRESSURE AT FROM ABOUT 50*C. TO 200*C.